Institut für Organische Chemie, Universität zu Köln, D-50939 Köln, Germany.
Beilstein J Org Chem. 2007 Oct 26;3:36. doi: 10.1186/1860-5397-3-36.
Electronic differentiations in Pd-catalyzed allylic substitutions are assessed computationally from transition structure models with electronically modified phospha-benzene-pyridine ligands. Although donor/acceptor substitutions at P and N ligand sites were expected to increase the site selectivity, i.e. the preference for "trans to P" attack at the allylic intermediate, acceptor/acceptor substitution yields the highest selectivity. Energetic and geometrical analyses of transition structures show that the sensitivity for electronic differentiation is crucial for this site selectivity. Early transition structures with acceptor substituted ligands give rise to more intensive Pd-allyl interactions, which transfer electronic P,N differentiation of the ligand more efficiently to the allyl termini and hence yield higher site selectivities.
电子差异化在 Pd 催化的烯丙基取代反应中通过带有电子修饰的膦-苯并吡啶配体的过渡态模型进行计算评估。虽然预计 P 和 N 配体位点的供体/受体取代会增加位选择性,即对烯丙基中间体的“反式 P”攻击的偏好,但受体/受体取代会产生最高的选择性。过渡态结构的能量和几何分析表明,对电子差异化的敏感性对于这种位选择性至关重要。具有受体取代配体的早期过渡态结构会导致更强烈的 Pd-烯丙基相互作用,从而更有效地将配体的 P,N 电子差异化传递到烯丙基末端,从而产生更高的位选择性。